The particular exception message is telling you that the mentioned class is missing in the classpath. As the org.apache.commons.io package name hints, the mentioned class is part of the http://commons.apache.org/io project.
And indeed, Commons FileUpload has Commons IO as a dependency. You need to download and drop commons-io.jar in the /WEB-INF/lib as well.
See also:
- How to upload files to server using JSP/Servlet?
- How to add JAR libraries to WAR project without facing java.lang.ClassNotFoundException? Classpath vs Build Path vs /WEB-INF/lib
- How do I import the javax.servlet API in my Eclipse project?